1. Field of the Invention
The present invention concerns a method and device for monitoring a movement-controlled machine, such as a robot, with an electronically commutated drive motor whose real position is detected, and for which a commutation angle is predetermined based on its real position and a control variable, in particular a predetermined desired position.
2. Description of the Prior Art
Machine with a movement control (i.e. a movement predetermined by a controller), such as single- or multi-axis robots, frequently have one or more servo drives (servo actuators) that act on the respective movement axes.
Such servo drives include an electronically commutated electromotor, for example a permanently activated synchronous motor, and a convertor to generate a rotating stator field that follows the permanently activated rotor and thus delivers a desired torque or a desired axle position. For this purpose, the commutation angle is predetermined that sets the orientation of the rotating stator field. It depends on, among other things, the real position of the rotor (i.e. its orientation), that can be detected, for example using Hall sensors or the induction in currentless stator windings. Activations of electronically commutating electromotors with a specification of an angle for the stator field are known from EP 1 734 648 A1, DE 103 30 551 B4 and DE 10 2007 040 560 A1, for example.
The servo-electronics that implement this operation and feeds the stator windings with current in the required manner is activated by a superordinate (i.e., higher in a hierarchical control architecture machine controller that predetermines a control variable for the drive motor on the basis of the movement control for the machine. For example, a robot controller can predetermine synchronized, new desired angle positions for the drive motors in order to achieve programmed desired poses.
Particularly in the case of manipulators (such as industrial robots, for instance) it should be ensured that predetermined velocity limits of individual axes or a reference point, such as the TCP (“Tool Center Point”), are not exceeded. Today this is ensured by appropriate velocity monitors in the robot controller, that detect real positions or real velocities, and compare these with predetermined velocity limits (possibly after corresponding time difference calculation) and triggers error reactions (for instance safely halts the robot) if the limits are exceeded.
This monitoring in the superordinate controller causes accumulating reaction times between exceeding a velocity limit and the corresponding reaction, such that an unwanted coasting of the robot occurs that must be accounted for with, for example, appropriately enlarged protective areas (i.e. areas free of objects and personnel)